This invention relates generally to semiconductor materials and, more particularly, to direct-gap semiconductors and related alloy heterostructures based on Si, Ge and Sn.
It has been known for many years—on theoretical grounds—that the Sn—Ge alloy system and the Si—Ge—Sn ternary alloy should have very interesting properties, especially as infrared devices. This has stimulated intense experimental efforts to grow such compounds, but for many years the resulting material quality has been incompatible with device applications.
The physical properties of most semiconductor alloys are smooth functions of their composition, providing a very versatile tool for device engineering. Alloys of elemental semiconductors such as Si and Ge, and alloys of III-V compounds such GaAs, AlAs, InAs, and InP, play a key role in high-speed microelectronics (see, e.g., E. H. Parker and T. E. Whall, Solid State Electronics 43, 1497 (1999)) and in optoelectronics (see, e.g., M. Quillec, in Critical Issues in Semiconductor Materials and Processing Technologies (Kluwer Academic Publishers, Dordrecht, Netherlands, NATO Advanced Study Institute on Semiconductor Materials and Processing Technologies, 1992)). In particular, the group-IV GexSi1-x system is a nearly ideal semiconductor alloy, with a lattice constant and interband optical transition energies that are essentially linear functions of x. See O. Madelung, Semiconductors—basic data (Springer, Berlin, N. Y., 1996).
An even more intriguing group-IV alloy is the Ge1-xSnx system. Group-IV semiconductors are notorious for not displaying a direct band gap, which precludes their use as active layers in light-emitting diodes and lasers. The band gap of the Ge1-xSnx alloy, however, is expected to undergo an indirect-to-direct transition, since the direct band gap has a value of 0.81 eV in Ge and becomes negative (−0.4 eV) in gray (α-) Sn. See M. L. Cohen and J. R. Chelikowsky, Electronic Structure and Optical Properties of Semiconductors (Springer, Heidelberg, Berlin, N.Y., 1989).
We previously have achieved successful formation of Ge1-xSnx films, which has prompted us to undertake exploratory research aimed at synthesis of the experimentally unknown Si—Ge—Sn ternary analog. This ternary system offers the potential of band gap and strain engineering and tuning of the optical properties of the system, as indicated by theoretical studies conducted by Soref and Perry as well Johnson and Ashcroft. (R. A. Soref and C. H. Perry, J. Appl. Phys. 69, 539 (1991); K. A. Johnson and N. W. Ashcroft, Phys. Rev. B 54, 14480 (1996).
It is an object of the present invention, therefore, to provide device-quality SixSnyGe1-x-y semiconductor materials and a procedure for synthesizing such materials.
Additional objects and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by the instrumentalities and combinations pointed out herein.